El Limón Waterfall is only 30 minutes away in the direction of Santa Barbara de Samaná (the main town of the Peninsula of Samaná) and certainly worth a trip. You probably want to join a tour.
Typically the tour (horse, guide, and lunch) costs per person between US$35 and US$50. We recommend Spanish-owned Santí Excursiones. It is a good choice but also a more expensive one. The lunch is excellent and the guides and staff are all adults. Follow the link at the bottom for more information.
You may also try “Parada La Manzana” or “Franklin”, just another 5km east of El Limón. They are closer to the falls, which means a shorter horseback ride. For some that may be a disadvantage… They will charge around USD 7 for the horseback ride only and USD 14 including lunch. When you get to these “Paradas”, order the lunch before going to the waterfall. They know how long you take to come back and will have the meal ready for you. We normally do it this way. A little tip for the guides should be considered.
On your way back to Las Terrenas stop at “Balcones del Atlántico”. You can’t miss it, it’s quite a big hotel, just before getting to the village of Las Terrenas. At the bar “Balconcito” they make wonderful drinks directly on the beach. It is a small, cozy wooden beach bar perfect for that sunset mojito. After the main entrance, just drive another 50 meters. You will see the sign of Balconcito. Should you be hungry again, consider the restaurant Porto at the same location. Fantastic location, good food, and in case you have to wait for a table, there is another, bigger bar here as well.